a) Name three things, related to the polymer chains (excluding positioning of si
ID: 509540 • Letter: A
Question
a) Name three things, related to the polymer chains (excluding positioning of side groups) and their packing, that has a strong affect on the mechanical properties of a in bulk form. b) Name two things, related to the external environment and applied loading, that has a strong affect the mechanical behaviour of a polymer in bulk form. c) The molecular weight of one polymer chain is M = 50, 400 g/mol and the degree of polymerization is 1, 200. Is the polymer PE (C_2H_4)_n, PVC (C_2ClH_3)n, PP (C_3H_6)_n or PTFE (C_2F_4)_n? Justify your answer. d) Polymer A has a melting temperature of 200C and a glass transition temperature of 143C. Polymer B has no melting temperature but a glass transition temperature of 120C. What can you conclude about the degree of crystallinity of polymers A and B (at room temperature)? e) For a thermoplastic polymer that behaves in a visco-elastic manner: i) sketch the stress as a function of time if you apply a strain at time zero and hold it constant of time if you apply a stress at time zero and hold it constant for a time delta t and then quickly reduce it to zero, ii) Sketch the stress as a function of time if you apply a strain at time zero and hold it constant for a time delta t and then quickly reduce it to zero.Explanation / Answer
(c)
M=XM0
Where M0 =Molar mass of repeating unit
M0=50400/1200=42 gm/mol
So it is MW of C3H6
So this is PP.
(a)
A polymer system is a set of polymer chains. A chain is composed of hard-spheres joined with each other in rigid groups. Each sphere represents an atom or a monomer.
Long polymer chains can have a hard time crystallizing, however, since the individual chains get tangled up and need to untangle to make a regular crystalline array. This is particularly true if the polymer melt is very viscous or if there are substituents on the chain that do not pack very well in the solid state.
Crystalline polymers usually contain regions of well-packed chains separated by amorphous regions. Pulling a fiber of a linear polymer causes the chains to line up, and can induce crystallization. This phenomenon occurs, for example, when you pull slowly on a polyethylene sixpack harness. Snapping the plastic abruptly apart (before stretching it) is easier, because the chains don't have time to orient.
At low temperatures, the tangled polymer chains tend to behave as rigid glasses.
The tacticity of a polymer chain can have a major influence on its properties. Atactic polymers, for example, being more disordered, cannot crystallize.
(b)
Thermal conductivity of polymer changed due to external environment.
t is possible that the polymer's ability to undergo larger non-linear deformation at lower rates of strain is suppressed when it is subjected to impact rates of loading.
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